Memory element and memory apparatus

ABSTRACT

According to some aspects, a layered structure includes a memory layer, a magnetization-fixed layer, and a tunnel insulating layer. The memory layer has magnetization perpendicular to a film face in which a direction of the magnetization is configured to be changed according to information by applying a current in a lamination direction of the layered structure. The magnetization-fixed layer has magnetization parallel or antiparallel to the magnetization direction of the memory layer and comprises a laminated ferripinned structure including a plurality of ferromagnetic layers and one or more non-magnetic layers, and includes a layer comprising an antiferromagnetic material formed on a first ferromagnetic layer of the plurality of ferromagnetic layers and situated between the first ferromagnetic layer and the non-magnetic layer. The tunnel insulating layer is located between the memory layer and the magnetization-fixed layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit under 35U.S.C. §120 of U.S. patent application Ser. No. 13/675,328, titled“MEMORY ELEMENT AND MEMORY APPARATUS,” filed on Nov. 13, 2012, now U.S.Pat. No. 8,842,465, which claims priority under 35 U.S.C. §119 toJapanese Patent Application JP 2011-263508, filed on Dec. 1, 2011. Theentire contents of these applications are hereby incorporated byreference in their entireties.

BACKGROUND

The present disclosure relates to a memory element and a memoryapparatus that have a plurality of magnetic layers and make a recordusing a spin torque magnetization switching.

Along with a rapid development of various information apparatuses frommobile terminals to large capacity servers, further high performanceimprovements such as higher integration, increases in speed, and lowerpower consumption have been pursued in elements such as a memory elementand a logic element configuring the apparatuses. Particularly, asemiconductor non-volatile memory has significantly progressed, and, asa large capacity file memory, a flash memory is spreading at such a ratethat hard disk drives are replaced with the flash memory. Meanwhile, thedevelopment of FeRAM (Ferroelectric Random Access Memory), MRAM(Magnetic Random Access Memory), PCRAM (Phase-Change Random AccessMemory), or the like has progressed as a substitute for the current NORflash memory, DRAM or the like in general use, in order to use them forcode storage or as a working memory. A part of these is already inpractical use.

Among them, the MRAM performs the data storage using a magnetizationdirection of a magnetic material so that high speed and nearly unlimited(10¹⁵ times or more) rewriting can be made, and therefore has alreadybeen used in fields such as industrial automation and an airplane. TheMRAM is expected to be used for code storage or a working memory in thenear future due to the high-speed operation and reliability. However,the MRAM has challenges related to lowering power consumption andincreasing capacity. This is a basic problem caused by the recordingprinciple of the MRAM, that is, the method of switching themagnetization using a current magnetic field generated from aninterconnection.

As a method of solving this problem, a recording method not using thecurrent magnetic field, that is, a magnetization switching method, isunder review. Particularly, research on a spin torque magnetizationswitching has been actively made (for example, see Japanese UnexaminedPatent Application Publication Nos. 2003-017782 and 2008-227388, U.S.Pat. No. 6,256,223, Physical Review B, 54, 9353(1996), Journal ofMagnetism and Magnetic Materials, 159, L1(1996)).

The memory element using a spin torque magnetization switching oftenincludes an MTJ (Magnetic Tunnel Junction) similarly as the MRAM.

This configuration uses a phenomenon in which, when spin-polarizedelectrons passing through a magnetic layer which is fixed in anarbitrary direction enter another free (the direction is not fixed)magnetic layer, a torque (which is also called as a spin transfertorque) is applied to the magnetic layer, and the free magnetic layer isswitched when a current having a predetermined threshold value or moreflows. The rewriting of 0/1 is performed by changing the polarity of thecurrent.

An absolute value of a current for the switching is 1 mA or less in thecase of a memory element with a scale of approximately 0.1 μm. Inaddition, since this current value decreases in proportion to a volumeof the element, scaling is possible. In addition, since a word linenecessary for the generation of a recording current magnetic field inthe MRAM is not necessary, there is an advantage that a cell structurebecomes simple.

Hereinafter, the MRAM utilizing a spin torque magnetization switchingwill be referred to as a Spin Torque-Magnetic Random Access Memory(ST-MRAM). The spin torque magnetization switching is also referred toas a spin injection magnetization switching. Great expectations are puton the ST-MRAM as a non-volatile memory capable of realizing lowerpower-consumption and larger capacity while maintaining the advantagesof the MRAM in which high speed and nearly unlimited rewriting may beperformed.

SUMMARY

In the MRAM, writing interconnections (word lines and bit lines) aredisposed separately from the memory element, and information is written(recorded) by a current magnetic field generated by applying a currentto the writing interconnections. Thus, the current necessary for writingcan sufficiently flow through the writing interconnections.

On the other hand, in the ST-MRAM, it is necessary that the currentflowing to the memory element induces the spin torque magnetizationswitching to switch the magnetization direction of the memory layer.

The information is written (recorded) by applying a current directly tothe memory element in this manner. In order to select a memory cell towhich writing is made, the memory element is connected to a selectiontransistor to configure the memory cell. In this case, the currentflowing to the memory element is limited by the amount of the currentthat can flow to the selection transistor, i.e., by the saturationcurrent of the selection transistor.

Thus, it is necessary to perform writing with a current equal to or lessthan the saturation current of the selection transistor, and it is knownthat the saturation current of the transistor decreases along withminiaturization. In order to miniaturize the ST-MRAM, it is necessarythat spin transfer efficiency be improved and the current flowing to thememory element be decreased.

In addition, it is necessary to secure a high magnetoresistance changeratio to amplify a read-out signal. In order to realize this, it iseffective to adopt the above-described MTJ structure, that is, toconfigure the memory element in such a manner that an intermediate layerthat comes into contact with the memory layer is used as a tunnelinsulating layer (tunnel barrier layer).

In the case where the tunnel insulating layer is used as theintermediate layer, the amount of the current flowing to the memoryelement is restricted to prevent the insulation breakdown of the tunnelinsulating layer from occurring. That is, the current necessary for thespin torque magnetization switching has to be restricted from theviewpoint of securing reliability with respect to repetitive writing ofthe memory element.

The current necessary for the spin torque magnetization switching isalso called as an switching current, a memory current or the like.

Also, since the ST-MRAM is a non-volatile memory, it is necessary tostably store the information written by a current. That is, it isnecessary to secure stability (thermal stability) with respect tothermal fluctuations in the magnetization of the memory layer.

In the case where the thermal stability of the memory layer is notsecured, an switched magnetization direction may be re-switched due toheat (temperature in an operational environment), which results in awriting error.

The memory element in the ST-MRAM is advantageous in scaling compared tothe MRAM in the related art, that is, advantageous in that the volume ofthe memory layer can be small, as described above in terms of arecording current value. However, as the volume is small, the thermalstability may be deteriorated as long as other characteristics are thesame.

As the capacity increase of the ST-MRAM proceeds, the volume of thememory element becomes smaller, such that it is important to secure thethermal stability.

Therefore, in the memory element of the ST-MRAM, the thermal stabilityis a significantly important characteristic, and it is necessary todesign the memory element in such a manner that the thermal stabilitythereof is secured even when the volume is decreased.

In other words, in order to provide the ST-MRAM as the non-volatilememory, the switching current necessary for the spin torquemagnetization switching is decreased so as not to exceed the saturationcurrent of the transistor or not to break the tunnel barrier. Also, itis necessary to secure the thermal stability for holding the writteninformation.

It is desirable to provide a memory element as an ST-MRAM thatsufficiently secures a thermal stability, which is an informationholding capacity.

According to an embodiment of the present disclosure, there is provideda memory element, including

a layered structure including

-   -   a memory layer having magnetization perpendicular to a film face        in which a magnetization direction is changed depending on        information,    -   a magnetization-fixed layer having magnetization perpendicular        to a film face that becomes a base of the information stored in        the memory layer, and    -   an intermediate layer that is formed of a non-magnetic material        and is provided between the memory layer and the        magnetization-fixed layer. The magnetization direction of the        memory layer is changed by applying a current in a lamination        direction of the layered structure to record the information in        the memory layer. In addition, the magnetization-fixed layer has        a laminated ferri-pinned structure including at least two        ferromagnetic layers and a non-magnetic layer, and includes an        anti-ferromagnetic oxide layer formed on any of the at least two        ferromagnetic layers.

A memory apparatus according to the embodiment of the present disclosureincludes a memory element holding information depending on amagnetization state of a magnetic material, and two types ofinterconnections intersected each other. The memory element is the onehaving the configuration as described above, and is disposed between thetwo types of the interconnections. Through the two types of theinterconnections, a current in a lamination direction flows to thememory element.

The memory element according to the embodiment of the present disclosureincludes the memory layer holding the information depending on themagnetization state of the magnetic material, and themagnetization-fixed layer formed on the memory layer via theintermediate layer. The information is recorded by switching themagnetization of the memory layer utilizing the spin torquemagnetization switching induced by the current flowing in the laminationdirection. Therefore, when the current is applied in the laminationdirection, the information can be recorded. Since the memory layer is aperpendicular magnetization film, a written current value necessary forswitching the magnetization direction of the memory layer can bedecreased.

The memory layer including the perpendicular magnetization film isdesirable in terms of decreasing the switching current and securing thethermal stability at the same time. For example, Nature Materials, 5,210(2006) suggests that when the perpendicular magnetization film suchas a Co/Ni multilayer film is used for the memory layer, decreasing theswitching current and securing the thermal stability can be provided atthe same time.

On the other hand, a perpendicular magnetization magnetic materialhaving interfacial magnetic anisotropy is favorably used for themagnetization-fixed layer. In particular, the magnetization-fixed layerin which Co or Fe is included under the intermediate layer (tunnelbarrier layer) is favorable to provide a high read-out signal. As themagnetization-fixed layer, a laminated ferri-pinned structure includingat least two ferromagnetic layers and a non-magnetic layer may be used.

When the magnetization-fixed layer has the laminated ferri-pinnedstructure, the asymmetry of the thermal stability in the informationwriting direction can be easily cancelled and the stability to the spintorque can be improved. Features demanded for the magnetization-fixedlayer include high strength of the laminated ferri-coupling when thesame magnetic layers are formed.

In this embodiment, in order to achieve the high strength of thelaminated ferri-coupling formed by a material having the perpendicularmagnetic anisotropy, an anti-ferromagnetic oxide layer is inserted nearthe non-magnetic layer. The ST-MRAM in which the asymmetry of thethermal stability in the information writing direction is low can beachieved by the magnetization-fixed layer having the high strength ofthe laminated ferri-coupling.

In addition, according to a configuration of the memory apparatus of theembodiment of the present disclosure, a current in the laminationdirection flows through the two types of interconnections to the memoryelement to induce a spin transfer. Thus, information can be recorded bythe spin torque magnetization switching when a current in the laminationdirection of the memory element flows through the two types ofinterconnections.

Also, since the thermal stability of the memory layer can besufficiently kept and the symmetry of the thermal stability in theinformation writing direction can be maintained, the informationrecorded in the memory element can be stably held, the memory apparatuscan be miniaturized, reliability can be enhanced, and power consumptioncan be decreased.

According to the embodiment of the present disclosure, the asymmetry ofthe thermal stability in the information writing direction can bedecreased by the magnetization-fixed layer having the high strength ofthe laminated ferri-coupling. Therefore, since the thermal stability,which is an information holding capacity, can be sufficiently secured,it is possible to configure the memory element having well-balancedproperties.

Thus, operation errors can be eliminated, and operation margins of thememory element can be fully provided. Accordingly, it is possible torealize a memory that stably operates with high reliability.

It is also possible to decrease a writing current and to decrease powerconsumption when writing into the memory element.

As a result, it is possible to decrease power consumption of the entirememory apparatus.

These and other objects, features and advantages of the presentdisclosure will become more apparent in light of the following detaileddescription of best mode embodiments thereof, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 an explanatory view of a memory apparatus according to anembodiment of the present disclosure;

FIG. 2 is a cross-sectional view of the memory apparatus according tothe embodiment;

FIGS. 3A to 3E are each an explanatory view of a configuration of amemory element according to the embodiment;

FIG. 4 is an explanatory diagram showing materials and film thicknessesof four experimental samples of memory elements;

FIGS. 5A and 5B are each a diagram showing the measurement result ofmagnetooptic Kerr effect of samples 1 and 2 in the experiment;

FIG. 6 is a diagram showing the measurement result of a magnetic fieldof a laminated ferri-coupling in the experimental samples;

FIGS. 7A and 7B are each an explanatory view of an application of theembodiment to a magnetic head.

DETAILED DESCRIPTION OF EMBODIMENTS

The embodiment of the present disclosure will be described in thefollowing order.

<1. Configuration of Memory Apparatus according to Embodiment>

<2. General Description of Memory Element according to Embodiment>

<3. Specific Configuration of Embodiment>

<4. Experiment>

<5. Alternative>

<1. Configuration of Memory Apparatus According to Embodiment>

Firstly, a configuration of a memory apparatus according to anembodiment of the present disclosure will be described.

FIGS. 1 and 2 each show a schematic diagram of the memory apparatusaccording to the embodiment. FIG. 1 is a perspective view and FIG. 2 isa cross-sectional view.

As shown in FIG. 1, in the memory apparatus according to the embodiment,a memory element 3 including an ST-MRAM that can hold informationdepending on a magnetization state is disposed in the vicinity of anintersection of two kinds of address interconnections (for example, aword line and a bit line) that are perpendicular with each other.

In other words, a drain region 8, a source region 7, and a gateelectrode 1 that make up a selection transistor for the selection ofeach memory apparatus are formed in a semiconductor substrate 10, suchas a silicon substrate, at portions isolated by an element isolationlayer 2. Among them, the gate electrode 1 functions also as an addressinterconnection (a word line) extending in the front-back direction inFIG. 1.

The drain region 8 is formed commonly with right and left selectiontransistors in FIG. 1, and an interconnection 9 is connected to thedrain region 8.

The memory element 3 having a memory layer that switches a magnetizationdirection of by a spin torque magnetization switching is disposedbetween the source region 7 and a bit line 6 that is disposed at anupper side and extends in the right-left direction in FIG. 1. The memoryelement 3 is configured with, for example, a magnetic tunnel junctionelement (MTJ element).

As shown in FIG. 2, the memory element 3 has two magnetic layers 15 and17. In the two magnetic layers 15 and 17, one magnetic layer is set as amagnetization-fixed layer 15 in which the direction of the magnetizationM15 is fixed, and the other magnetic layer is set as amagnetization-free layer in which the direction of the magnetization M17varies, that is, a memory layer 17.

In addition, the memory element 3 is connected to each bit line 6 andthe source region 7 through upper and lower contact layers 4,respectively.

In this manner, when a current in the vertical direction is applied tothe memory element 3 through the two types of address interconnections 1and 6, the direction of the magnetization M17 of the memory layer 17 canbe switched by a spin torque magnetization switching.

In such a memory apparatus, it is necessary to perform writing with acurrent equal to or less than the saturation current of the selectiontransistor, and it is known that the saturation current of thetransistor decreases along with miniaturization. In order to miniaturizethe memory apparatus, it is desirable that spin transfer efficiency beimproved and the current flowing to the memory element 3 be decreased.

In addition, it is necessary to secure a high magnetoresistance changeratio to amplify a read-out signal. In order to realize this, it iseffective to adopt the above-described MTJ structure, that is, toconfigure the memory element 3 in such a manner that an intermediatelayer is used as a tunnel insulating layer (tunnel barrier layer)between the two magnetic layers 15 and 17.

In the case where the tunnel insulating layer is used as theintermediate layer, the amount of the current flowing to the memoryelement 3 is restricted to prevent the insulation breakdown of thetunnel insulating layer from occurring. That is, it is desirable torestrict the current necessary for the spin torque magnetizationswitching from the viewpoint of securing reliability with respect torepetitive writing of the memory element 3. The current necessary forthe spin torque magnetization switching is also called as an switchingcurrent, a memory current or the like.

Also, since the memory apparatus is a non-volatile memory apparatus, itis necessary to stably store the information written by a current. Thatis, it is necessary to secure stability (thermal stability) with respectto thermal fluctuations in the magnetization of the memory layer.

In the case where the thermal stability of the memory layer is notsecured, an switched magnetization direction may be re-switched due toheat (temperature in an operational environment), which results in awriting error.

The memory element 3 (ST-MRAM) in the memory apparatus is advantageousin scaling compared to the MRAM in the related art, that is,advantageous in that the volume of the memory layer can be small.However, as the volume is small, the thermal stability may bedeteriorated as long as other characteristics are the same.

As the capacity increase of the ST-MRAM proceeds, the volume of thememory element 3 becomes smaller, such that it is important to securethe thermal stability.

Therefore, in the memory element 3 of the ST-MRAM, the thermal stabilityis a significantly important characteristic, and it is necessary todesign the memory element in such a manner that the thermal stabilitythereof is secured even when the volume is decreased.

<2. General Description of Memory Element According to Embodiment>

Then, a general description of the memory element 3 according to theembodiment will be described.

The memory element 3 according to the embodiment records information byswitching the magnetization direction of the memory layer by theabove-mentioned spin torque magnetization switching.

The memory layer is composed of a magnetic material including aferromagnetic layer, and holds the information depending on themagnetization state (magnetic direction) of the magnetic material.

The memory element 3 has a layered structure, for example, as shown inFIG. 3A, and includes the memory layer 17 and the magnetization-fixedlayer 15 as the at least two ferromagnetic layers, and an intermediatelayer 16 disposed between the two magnetic layers.

As shown in FIG. 3B, the memory element 3 may includemagnetization-fixed layers 15U and 15L as the at least two ferromagneticlayers, the memory layer 17, and intermediate layers 16U and 16Ldisposed between the three magnetic layers.

The memory layer 17 has magnetization perpendicular to a film face inwhich a magnetization direction is changed corresponding to theinformation.

The magnetization-fixed layer 15 has magnetization perpendicular to afilm face that becomes a base of the information stored in the memorylayer 17.

The intermediate layer 16 is formed of a non-magnetic material and isprovided between the memory layer 17 and the magnetization-fixed layer15.

By injecting spin polarized ions in a lamination direction of thelayered structure having the memory layer 17, the intermediate layer 16and the magnetization-fixed layer 15, the magnetization direction of thememory layer 17 is changed, whereby the information is stored in thememory layer 17.

Here, the spin torque magnetization switching will be briefly described.

For electrons there are two possible values for spin angular momentum.The states of the spin are defined temporarily as up and down. Thenumbers of up spin and down spin electrons are the same in thenon-magnetic material. But the numbers of up spin and down spinelectrons differ in the ferromagnetic material. In two ferromagneticlayers, i.e., the magnetization-fixed layer 15 and the memory layer 17,of the ST-MRAM, the case that the directions of the magnetic moment ofeach layer are in a reverse direction and the electrons are moved fromthe magnetization-fixed layer 15 to the memory layer 17 will beconsidered.

The magnetization-fixed layer 15 is a fixed magnetic layer having thedirection of the magnetic moment fixed by high coercive force.

The electrons passed through the magnetization-fixed layer 15 are spinpolarized, that is, the numbers of up spin and down spin electronsdiffers. When the thickness of the intermediate layer 16 that is thenon-magnetic layer is made to be sufficiently thin, the electrons reachthe other magnetic material, that is, the memory layer 17 before thespin polarization is mitigated by passing through themagnetization-fixed layer 15 and the electrons become a commonnon-polarized state (the numbers of up spin and down spin electrons arethe same) in a non-polarized material.

A sign of the spin polarization in the memory layer 17 is reversed sothat a part of the electrons is switched for lowering the system energy,that is, the direction of the spin angular momentum is changed. At thistime, the entire angular momentum of the system is necessary to beconserved so that a reaction equal to the total angular momentum changeby the electron, the direction of which is changed, is applied also tothe magnetic moment of the memory layer 17.

In the case where the current, that is, the number of electrons passedthrough per unit time is small, the total number of electrons, thedirections of which, are changed, becomes small so that the change inthe angular momentum occurring in the magnetic moment of the memorylayer 17 becomes small, but when the current is increased, it ispossible to apply large change in the angular momentum within a unittime.

The time change of the angular momentum with is a torque, and when thetorque exceeds a threshold value, the magnetic moment of the memorylayer 17 starts a precession, and rotates 180 degrees due to itsuniaxial anisotropy to be stable. That is, the switching from thereverse direction to the same direction occurs.

When the magnetization directions are in the same direction and theelectrons are made to reversely flow from the memory layer 17 to themagnetization-fixed layer 15, the electrons are then reflected at themagnetization-fixed layer 15. When the electrons that are reflected andspin-switched enter the memory layer 17, a torque is applied and themagnetic moment is switched to the reverse direction. However, at thistime, the amount of current necessary for causing the switching islarger than that in the case of switching from the reverse direction tothe same direction.

The switching of the magnetic moment from the same direction to thereverse direction is difficult to intuitively understand, but it may beconsidered that the magnetization-fixed layer 15 is fixed such that themagnetic moment is not switched, and the memory layer 17 is switched forconserving the angular momentum of the entire system. Thus, therecording of 0/1 is performed by applying a current having apredetermined threshold value or more, which corresponds to eachpolarity, from the magnetization-fixed layer 15 to the memory layer 17or in a reverse direction thereof.

Reading of information is performed by using a magnetoresistive effectsimilarly to the MRAM in the related art. That is, as is the case withthe above-described recording, a current is applied in a directionperpendicular to the film face. Then, a phenomenon in which anelectrical resistance shown by the element varies depending on whetheror not the magnetic moment of the memory layer 17 is the same or reversedirection to the magnetic moment of the magnetization-fixed layer 15 isused.

A material used for the intermediate layer 16 between themagnetization-fixed layer 15 and the memory layer 17 may be a metallicmaterial or an insulating material, but the insulating material may beused for the intermediate layer to obtain a relatively high read-outsignal (resistance change ratio), and to realize the recording by arelatively low current. The element at this time is called aferromagnetic tunnel junction (Magnetic Tunnel Junction: MTJ) element.

A threshold value Ic of the current necessary to reverse themagnetization direction of the magnetic layer by the spin torquemagnetization switching is different depending on whether an easy axisof magnetization of the magnetic layer is an in-plane direction or aperpendicular direction.

Although the memory element according to the embodiment hasperpendicular magnetization, in a memory element having an in-planemagnetization in the related art, the switching current for switchingthe magnetization direction of the magnetic layer is represented byIc_para. When the direction is switched from the same direction to thereverse direction, the equation holds,Ic_para=(A·α·Ms·V/g(0)/P)(Hk+2πMs).When the direction is switched from the reverse direction to the samedirection, the equation holds,Ic_para=−(A·α·Ms·V/g(π)/P)(Hk+2πMs).

The same direction and the reverse direction denote the magnetizationdirections of the memory layer based on the magnetization direction ofthe magnetization-fixed layer, and are also referred to as a paralleldirection and a non-parallel direction, respectively.

On the other hand, in the memory element having perpendicularmagnetization according to the embodiment, the switching current isrepresented by Ic_perp. When the direction is switched from the samedirection to the reverse direction, the equation holds,Ic_perp=(A·α·Ms·V/g(0)/P)(Hk−4πMs)When the direction is switched from the reverse direction to the samedirection, the equation holds,Ic_perp=−(A·α·Ms·V/g(π)/P)(Hk−4πMs)where A represents a constant, α represents a damping constant, Msrepresents a saturation magnetization, V represents an element volume, Prepresents a spin polarizability, g(0) and g(π) represent coefficientscorresponding to efficiencies of the spin torque transmitted to theother magnetic layer in the same direction and the reverse direction,respectively, and Hk represents the magnetic anisotropy.

In the respective equations, when the term (Hk−4πMs) in theperpendicular magnetization type is compared with the term (Hk+2πMs) inthe in-plane magnetization type, it can be understood that theperpendicular magnetization type is suitable to decrease a recordingcurrent.

Here, a relationship between an switching current Ic0 and a thermalstability index Δ is represented by the following [Equation 1].

${I_{C}0} = {( \frac{4e\; k_{B}T}{h -} )( \frac{\alpha\Delta}{\eta} )}$where e represents an electron charge, η represents spin injectionefficiency, h with bar represents a reduced Planck constant, αrepresents a damping constant, k_(B) represents Boltzmann constant, andT represents a temperature.

According to the embodiment, the memory element includes the magneticlayer (memory layer 17) capable of holding the information depending onthe magnetization state, and the magnetization-fixed layer 15 in whichthe magnetization direction is fixed.

The memory element has to hold the written information to function as amemory. An index of ability to hold the information is the thermalstability index Δ (=KV/k_(B)T). The Δ is represented by the (Equation2).

$\Delta = {\frac{KV}{k_{B}T} = \frac{M_{S}{VH}_{K}}{2k_{B}T}}$where Hk represents an effective anisotropic magnetic field, k_(B)represents Boltzmann constant, T represents a temperature, Ms representsa saturated magnetization amount, V represents a volume of the memorylayer, and K represents the anisotropic energy.

The effective anisotropic magnetic field Hk is affected by a shapemagnetic anisotropy, an induced magnetic anisotropy, a crystal magneticanisotropy and the like. Assuming a single-domain coherent rotationmodel, the Hk will be equal to coercive force.

The thermal stability index Δ and the threshold value Ic of the currenthave often the trade-off relationship. Accordingly, in order to maintainthe memory characteristics, the trade-off often becomes an issue.

In practice, in a circle TMR element having, for example, the memorylayer 17 with a thickness of 2 nm and a plane pattern with a diameter of100 nm, the threshold value of the current to change the magnetizationstate of the memory layer is about a hundred to hundreds μA.

In contrast, in the MRAM in the related art for switching themagnetization using a current magnetic field, the written currentexceeds several mA.

Accordingly, in the ST-MRAM, the threshold value of the written currentbecomes sufficiently low, as described above. It can be effective todecrease the power consumption of the integrated circuit.

In addition, since the interconnections for generating the currentmagnetic field generally used in the MRAM in the related art areunnecessary, the ST-MRAM is advantageous over the MRAM in the relatedart in terms of the integration.

When the spin torque magnetization switching is induced, a current isapplied directly into the memory element to write (record) theinformation. In order to select a memory cell to which writing is made,the memory element is connected to a selection transistor to configurethe memory cell.

In this case, the current flowing to the memory element is limited bythe amount of the current that can flow to the selection transistor,i.e., by the saturation current of the selection transistor.

In order to decrease the recording current, the perpendicularmagnetization is desirably used, as described above. Also, theperpendicular magnetization can generally provide higher magneticanisotropy than the in-plane magnetization type, and therefore isdesirable in that the Δ is kept greater.

Examples of the magnetic material having the perpendicular anisotropyinclude rare earth-transition metal alloys (such as TbCoFe), metalmultilayer films (such as a Co/Pd multilayer film), ordered alloys (suchas FePt), those utilizing interfacial magnetic anisotropy between anoxide and a magnetic metal (such as Co/MgO) and the like. When the rareearth-transition metal alloys are diffused and crystallized by beingheated, the perpendicular magnetic anisotropy is lost, and therefore therare earth-transition metal alloys are not desirable as an ST-MRAMmaterial.

It is known that also the metal multilayer film is diffused when beingheated, and the perpendicular magnetic anisotropy is degraded. Since theperpendicular magnetic anisotropy is developed when the metal multilayerfilm has a face-centered cubic (111) orientation, it may be difficult torealize a (001) orientation necessary for a high polarizability layerincluding MgO, and Fe, CoFe and CoFeB disposed adjacent to MgO. L10ordered alloy is stable even at high temperature and shows theperpendicular magnetic anisotropy in the (001) orientation. Therefore,the above-mentioned problem is not induced. However, the L10 orderedalloy has to be heated at sufficiently high temperature of 500° C. ormore during the production, or atoms should be arrayed regularly bybeing heated at a high temperature of 500° C. or more after theproduction. It may induce undesirable diffusion or an increase ininterfacial roughness in other portions of a laminated film such as atunnel barrier.

In contrast, the material utilizing interfacial magnetic anisotropy,i.e., the material including MgO as the tunnel barrier and a Co or Fematerial laminated thereon hardly induces any of the above-mentionedproblems, and is therefore highly expected as the memory layer materialof the ST-MRAM.

On the other hand, a perpendicular magnetization magnetic materialhaving interfacial magnetic anisotropy is favorably used for themagnetization-fixed layer 15. In particular, the magnetization-fixedlayer 15 in which Co or Fe is included under the intermediate layer (forexample, MgO layer) that is the tunnel barrier is favorable to provide ahigh read-out signal. The magnetization-fixed layer 15 may be asingle-layer or may have a laminated ferri-pinned structure including atleast two ferromagnetic layers and a non-magnetic layer may be used.Typically, the laminated ferri-pinned structure including at least twoferromagnetic layers and a non-magnetic layer (Ru) is used.

The advantages of the magnetization-fixed layer 15 having the laminatedferri-pinned structure include that the asymmetry of the thermalstability in the information writing direction can be easily cancelledand that the stability to the spin torque can be improved.

Features demanded for the magnetization-fixed layer 15 include highstrength of the laminated ferri-coupling when the same magnetic layersare formed.

The studies by the inventors have revealed that, in order to achieve thehigh strength of the laminated ferri-coupling formed by a materialhaving the perpendicular magnetic anisotropy, it is important to insertan anti-ferromagnetic oxide layer into the ferromagnetic layer of themagnetization-fixed layer 15.

Specifically, the magnetization-fixed layer 15 has a laminatedferri-pinned structure of the ferromagnetic layer of the perpendicularmagnetization film/the non-magnetic layer/the ferromagnetic layer of theperpendicular magnetization film. Then, an anti-ferromagnetic oxidelayer is formed on any of the ferromagnetic layers.

For example, the magnetization-fixed layer 15 has a structure of theperpendicular magnetization film/the non-magnetic layer/theanti-ferromagnetic oxide layer/a material having the perpendicularmagnetic anisotropy arising from the interfacial magnetic anisotropy,i.e., Co—Fe—B.

Alternatively, the magnetization-fixed layer 15 has a structure of theanti-ferromagnetic oxide layer/the perpendicular magnetization film/thenon-magnetic layer/a material having the perpendicular magneticanisotropy arising from the interfacial magnetic anisotropy, i.e.,Co—Fe—B.

These increase the strength of the laminated ferri-coupling.

In the embodiment, the memory layer 17 is a perpendicular magnetizationfilm of Co—Fe—B.

In view of the saturated current value of the selection transistor, asthe non-magnetic intermediate layer 16 between the memory layer 17 andthe magnetization-fixed layer 15, the magnetic tunnel junction (MTJ)element is configured using the tunnel insulating layer including aninsulating material.

The magnetic tunnel junction (MTJ) element is configured by using thetunnel insulating layer, such that it is possible to make amagnetoresistance change ratio (MR ratio) high compared to a case wherea giant magnetoresistive effect (GMR) element is configured by using anon-magnetic conductive layer, and therefore it is possible to increaseread-out signal strength.

In particular, when magnesium oxide (MgO) is used as the material of theintermediate layer 16 as the tunnel insulating layer, it is possible tomake the magnetoresistance change ratio (MR ratio) high.

In addition, generally, the spin transfer efficiency depends on the MRratio, and as the MR ratio is high, the spin transfer efficiency isimproved, and therefore it is possible to decrease the magnetizationswitching current density.

Therefore, when magnesium oxide is used as the material of the tunnelinsulating layer and the memory layer 17 is used, it is possible todecrease the writing threshold current by the spin torque magnetizationswitching and therefore it is possible to perform the writing(recording) of information with a small current. In addition, it ispossible to increase the read-out signal strength.

In this manner, it is possible to decrease the writing threshold currentby the spin torque magnetization switching by securing the MR ratio (TMRratio), and it is possible to perform the writing (recording) ofinformation with a small current. In addition, it is possible toincrease the read-out signal strength.

As described above, in the case where the tunnel insulating layer isformed of the magnesium oxide (MgO) film, it is desirable that the MgOfilm be crystallized and a crystal orientation be maintained in the(001) direction.

In this embodiment, in addition to a configuration formed of themagnesium oxide, the intermediate layer 16 (tunnel insulating layer)disposed between the memory layer 17 and the magnetization-fixed layer15 may be configured by using, for example, various insulatingmaterials, dielectric materials, and semiconductors such as aluminumoxide, aluminum nitride, SiO₂, Bi₂O₃, MgF₂, CaF, SrTiO₂, AlLaO₃, andAl—N—O.

An area resistance value of the tunnel insulating layer has to becontrolled to several tens Ωμm² or less from the viewpoint of obtaininga current density necessary for switching the magnetization direction ofthe memory layer 17 by the spin torque magnetization switching.

In the tunnel insulating layer including the MgO film, the thickness ofthe MgO film has to be set to 1.5 nm or less so that the area resistancevalue is in the range described above.

Adjacent to the memory layer 17, a cap layer 18 is disposed. The caplayer 18 includes Ta or Ru, for example, and the interface of the caplayer 18, which comes into contact with the memory layer 17, may includean oxide. As the oxide of the cap layer 18, MgO, aluminum oxide, TiO₂,SiO₂, Bi₂O₃, SrTiO₂, AlLaO₃, and Al—N—O may be used, for example.

In addition, it is desirable to make the memory element 3 small in sizeto easily switch the magnetization direction of the memory layer 17 witha small current.

Therefore, the area of the memory element 3 is desirably set to 0.01 μm²or less.

In addition, a non-magnetic element may be added to the memory layer 17.

When heterogeneous elements are added, there is obtained an effect suchas improvement in a heat resistance or increase in a magnetoresistiveeffect due to the prevention of diffusion, and increase in dielectricstrength voltage accompanied with planarization. As a material of thisadded element, B, C, N, O, F, Mg, Si, P, Ti, V, Cr, Mn, Ni, Cu, Ge, Nb,Ru, Rh, Pd, Ag, Ta, Ir, Pt, Au, Zr, Hf, W, Mo, Re, Os, or an alloy oroxide thereof may be used.

In addition, as the memory layer 17, a ferromagnetic layer with adifferent composition may be directly laminated. In addition, aferromagnetic layer and a soft magnetic layer may be laminated, or aplurality of ferromagnetic layers may be laminated through the softmagnetic layer or a non-magnetic layer. In the case of laminating inthis manner, it is possible to obtain an effect according to theembodiment of the present disclosure.

In particular, in the case where the plurality of ferromagnetic layersis laminated through the non-magnetic layer, it is possible to adjustthe interaction strength between the ferromagnetic layers, and thereforean effect capable of controlling a magnetization switching current notto increase is obtained. As a material of the non-magnetic layer in thiscase, Ru, Os, Re, Ir, Au, Ag, Cu, Al, Bi, Si, B, C, Cr, Ta, Pd, Pt, Zr,Hf, W, Mo, Nb, or an alloy thereof may be used.

It is desirable that the film thickness of each of themagnetization-fixed layer 15 and the memory layer 17 be 0.5 nm to 30 nm.

Other configuration of the memory element may be the same as theconfiguration of a memory element that records information by the spintorque magnetization switching in the related art.

The magnetization-fixed layer 15 may be configured in such a manner thatthe magnetization direction is fixed by only a ferromagnetic layer or byusing an antiferromagnetic coupling of an antiferromagnetic layer and aferromagnetic layer.

As a material of the ferromagnetic layer making up themagnetization-fixed layer 15 having the laminated ferri-pinnedstructure, Co, CoFe, CoPt, CoFeB, or the like may be used. In addition,as a material of the non-magnetic layer, Ru, Cr, Re, Ir, Os, or the likemay be used.

As a material of the antiferromagnetic layer, a magnetic material suchas an FeMn alloy, a PtMn alloy, a PtCrMn alloy, an NiMn alloy, an IrMnalloy, NiO, and Fe₂O₃ may be exemplified.

In addition, a magnetic characteristic may be adjusted by adding anon-magnetic element such as Ag, Cu, Au, Al, Si, Bi, Ta, B, C, O, N, Pd,Pt, Zr, Ta, Hf, Ir, W, Mo, and Nb to the above-described magneticmaterials, or in addition to this, a crystalline structure or variousphysical properties such as a crystalline property and a stability of asubstance may be adjusted.

In addition, in relation to a film configuration of the memory element3, there is no problem if the memory layer 17 may be disposed at thelower side of the magnetization-fixed layer 15. In other words, thepositions of the memory layer 17 and the magnetization-fixed layer 15are switched different from FIG. 3A.

<3. Specific Configuration of Embodiment>

Subsequently, a specific configuration of this embodiment will bedescribed.

The memory apparatus includes the memory element 3, which can holdinformation depending on a magnetization state, disposed in the vicinityof an intersection of two kinds of address interconnections 1 and 6 (forexample, a word line and a bit line) that are perpendicular to eachother, as shown in FIGS. 1 and 2.

When a current in the vertical direction is applied to the memoryelement 3 through the two types of address interconnections 1 and 6, themagnetization direction of the memory layer 17 can be switched by thespin torque magnetization switching.

FIGS. 3A and 3B each show an example of the layered structure of thememory element 3 (ST-MRAM) according to the embodiment.

In the memory element 3 having the structure shown in FIG. 3A, theunderlying layer 14, the magnetization-fixed layer 15, the intermediatelayer 16, the memory layer 17 and the cap layer 18 are laminated in thestated order from the bottom.

In this case, the magnetization-fixed layer 15 is disposed under thememory layer 17 in which the direction of the magnetization M17 isswitched by the spin injection.

In regard to the spin injection memory, “0” and “1” of information aredefined by a relative angle between the magnetization M17 of the memorylayer 17 and the magnetization M15 of the magnetization-fixed layer 15.

The intermediate layer 16 that serves as a tunnel barrier layer (tunnelinsulating layer) is provided between the memory layer 17 and themagnetization-fixed layer 15, and an MTJ element is configured by thememory layer 17 and the magnetization-fixed layer 15.

The memory layer 17 is composed of a ferromagnetic material having amagnetic moment in which the direction of the magnetization M17 isfreely changed in a direction perpendicular to a film face. Themagnetization-fixed layer 15 is composed of a ferromagnetic materialhaving a magnetic moment in which the direction of the magnetization M15is freely changed in a direction perpendicular to a film face.

Information is stored by the magnetization direction of the memory layer17 having uniaxial anisotropy. Writing is made by applying a current inthe direction perpendicular to the film face, and inducing the spintorque magnetization switching. Thus, the magnetization-fixed layer 15is disposed under the memory layer 17 in which the magnetizationdirection is switched by the spin injection, and is to serve as the baseof the stored information (magnetization direction) of the memory layer17.

In the embodiment, Co—Fe—B is used for the memory layer 17 and themagnetization-fixed layer 15.

It should be noted that the memory layer 17 may include the non-magneticlayer in addition to the Co—Fe—B magnetic layer. The non-magnetic layerincludes Ta, V, Nb, Cr, W, Mo, Ti, Zr and Hf, for example.

Since the magnetization-fixed layer 15 is the base of the information,the magnetization direction should not be changed by recording orreading-out. However, the magnetization-fixed layer 15 does notnecessarily need to be fixed to the specific direction, and only needsto be difficult to move by increasing the coercive force, the filmthickness or the magnetic damping constant as compared with the memorylayer 17.

The intermediate layer 16 is formed of a magnesium oxide (MgO) layer,for example. In this case, it is possible to make a magnetoresistancechange ratio (MR ratio) high.

When the MR ratio is thus made to be high, the spin injection efficiencyis improved, and therefore it is possible to decrease the currentdensity necessary for switching the direction of the magnetization M17of the memory layer 17.

The intermediate layer 16 may be configured by using, for example,various insulating materials, dielectric materials, and semiconductorssuch as aluminum oxide, aluminum nitride, SiO₂, MgF₂, CaF, SrTiO₂,AlLaO₃, and Al—N—O, as well as magnesium oxide.

As the underlying layer 14 and the cap layer 18, a variety of metalssuch as Ta, Ti, W, and Ru and a conductive nitride such as TiN can beused. In the underlying layer 14 and the cap layer 18, a single layermay be used or a plurality of layers including different materials maybe laminated.

Next, FIG. 33 shows a dual layered structure according to theembodiment.

In the memory element 3, the underlying layer 14, the lowermagnetization-fixed layer 15L, the lower intermediate layer 16L, thememory layer 17, the upper intermediate layer 16U, the uppermagnetization-fixed layer 15U, and the cap layer 18 are laminated in thestated order from the bottom.

In other words, the memory layer 17 is sandwiched between themagnetization-fixed layers 15U and 15L via the intermediate layers 16Uand 16L.

In such a dual structure, the magnetization directions of themagnetization-fixed layers 15U and 15L are necessary not to be changed(magnetization M15U of the upper magnetization-fixed layer 15U andmagnetization M15L of the lower magnetization-fixed layer 15L arereversely directed).

According to the above-described embodiment shown in FIGS. 3A and 3B,the memory layer 17 of the memory element 3 is configured in such amanner that the magnitude of the effective diamagnetic field that thememory layer 17 receives is smaller than the saturated magnetizationamount Ms of the memory layer 17.

In other words, the effective diamagnetic field that the memory layer 17receives is decreased smaller than the saturated magnetization amount Msof the memory layer 17 by selecting the ferromagnetic material Co—Fe—Bcomposition of the memory layer 17.

The memory element 3 of the embodiment can be manufactured bycontinuously forming from the underlying layer 14 to the cap layer 18 ina vacuum apparatus, and then by forming a pattern of the memory element3 by a processing such as a subsequent etching.

The memory element 3A shown in FIG. 3 has a laminated ferri-pinnedstructure in which the magnetization-fixed layer 15 has at least twoferromagnetic layers and a non-magnetic layer.

Moreover, the memory element 3 shown in FIG. 3B has a laminatedferri-pinned structure in which at least one of the magnetization-fixedlayers 15U and 15L has at least two ferromagnetic layers and anon-magnetic layer.

In both of the examples of FIGS. 3A and 3B, an anti-ferromagnetic oxidelayer is formed on the ferromagnetic layer of the magnetization-fixedlayer 15.

As the anti-ferromagnetic oxide layer, a layer including Co—O isinserted. This Co—O may be formed by direct sputtering, or may beobtained by oxidizing Co included in the ferromagnetic layer.

FIGS. 3C, 3D, and 3E each show a configuration example of themagnetization-fixed layer 15 according to this embodiment, i.e., anexample of a laminated ferri-pinned structure in which ananti-ferromagnetic oxide layer including Co—C is inserted.

FIG. 3C shows an example of the magnetization-fixed layer 15 in whichthe ferromagnetic layer 15 c, the non-magnetic layer 15 b, theanti-ferromagnetic oxide layer 15 d, and the ferromagnetic layer 15 aare laminated in the stated order from the bottom.

FIG. 3D shows an example of the magnetization-fixed layer 15 in whichthe ferromagnetic layer 15 c, the anti-ferromagnetic oxide layer 15 d,the non-magnetic layer 15 b, and the ferromagnetic layer 15 a arelaminated in the stated order from the bottom.

FIG. 3E shows an example of the magnetization-fixed layer 15 in whichthe anti-ferromagnetic oxide layer 15 d, the ferromagnetic layer 15 c,the non-magnetic layer 15 b, and the ferromagnetic layer 15 a arelaminated in the stated order from the bottom.

In any of the examples of FIGS. 3C, 3D, and 3E, the ferromagnetic layer15 a, which comes into contact with the intermediate layer 16, is theCo—Fe—B magnetic layer, for example. The ferromagnetic layer 15 c, whichcomes into contact with the underlying layer 14, is formed of CoPt, forexample.

In the example of FIG. 3C, for example, the anti-ferromagnetic oxidelayer 15 d (Co—O) may be formed by sputtering after the non-magneticlayer 15 b is laminated, or may be formed by oxidizing Co included inthe ferromagnetic layer 15 a at the interface when the ferromagneticlayer 15 a is formed.

Moreover, in the example of FIG. 3D, the anti-ferromagnetic oxide layer15 d may be formed by sputtering after the non-magnetic layer 15 c islaminated, or may be formed by oxidizing Co included in the surface ofthe ferromagnetic layer 15 c when the ferromagnetic layer 15 c isformed.

Moreover, in the example of FIG. 3E, the anti-ferromagnetic oxide layer15 d may be formed by sputtering before the non-magnetic layer 15 c islaminated, or may be formed by oxidizing Co included in theferromagnetic layer 15 c at the interface when the ferromagnetic layer15 c is formed.

It should be noted that the magnetization-fixed layer 15 is the same asthose shown in FIGS. 3C, 3D, and 3E in the case where the layeredstructure is a dual structure shown in FIG. 3B and the lowermagnetization-fixed layer 15L has a laminated ferri-pinned structure. Inthe case where the upper magnetization-fixed layer 15U has a laminatedferri-pinned structure, it is only necessary to turn the layeredstructures shown in FIGS. 3C, 3D, and 3E upside down.

Since the magnetization-fixed layer 15 has the laminated ferri-pinnedstructure including the two ferromagnetic layers 15 a and 15 c and thenon-magnetic layer 15 b, and the anti-ferromagnetic oxide layer 15 d isformed on any of the ferromagnetic layers (15 a or 15 b), as shown inFIGS. 3C, 3D, and 3E, the strength of the laminated ferri-coupling isincreased. Moreover, the ferromagnetic layer 15 a, which comes intocontact with the intermediate layer 16, is formed of a material havingthe perpendicular magnetic anisotropy arising from the interfacialmagnetic anisotropy, i.e., Co—Fe—B. Also this contributes the increasingeffect. Thus, since the strength of the laminated ferri-coupling isincreased, the memory element 3 having low asymmetry of the thermalstability can be configured.

According to the above-described embodiment, since the memory layer 17of the memory element 3 is the perpendicular magnetization film, awriting current necessary for switching the magnetization M17 directionof the memory layer 17 can be decreased.

In particular, since the magnetization-fixed layer 15 has the laminatedferri-pinned structure including the two ferromagnetic layers 15 a and15 c, the non-magnetic layer 15 b and the anti-ferromagnetic oxide layer15 d, and the ferromagnetic layer 15 a is the perpendicularmagnetization film of the material having the perpendicular magneticanisotropy arising from the interfacial magnetic anisotropy, i.e.,Co—Fe—B perpendicular magnetic film, the memory element 3 having highstrength of the laminated ferri-coupling and low asymmetry of thethermal stability can be configured.

Thus, since the thermal stability, which is an information holdingcapacity, can be sufficiently secured, it is possible to configure thememory element having well-balanced properties.

In this manner, operation errors can be eliminated, and operationmargins of the memory element 3 can be sufficiently obtained, such thatit is possible to stably operate the memory element 3.

Accordingly, it is possible to realize a memory that stably operateswith high reliability.

It is also possible to decrease a writing current and to decrease powerconsumption when writing into the memory element 3.

As a result, it is possible to decrease power consumption of the entirememory apparatus in which a memory cell is configured by the memoryelement 3 of this embodiment.

Therefore, in regard to the memory including the memory element 3capable of realizing a memory that is excellent in the informationholding capacity and stably operates with high reliability, it ispossible to decrease the power consumption.

In addition, the memory apparatus that includes the memory element 3shown in FIG. 3 and has a configuration shown in FIG. 1 has an advantagein that a general semiconductor MOS forming process may be applied whenthe memory apparatus is manufactured. Therefore, it is possible to applythe memory of this embodiment as a general purpose memory.

<4. Experiment>

Here, in regard to the configuration of the memory element 3 accordingto this embodiment shown in FIG. 3, samples were manufactured, and thencharacteristics thereof were examined.

In an actual memory apparatus, as shown in FIG. 1, a semiconductorcircuit for switching or the like is present in addition to the memoryelement 3, but here, the examination was made on a wafer in which onlythe magnetization-fixed layer is formed for the purpose of investigatingthe magnetization switching characteristic of the magnetization-fixedlayer 15.

A thermally-oxidized film having a thickness of 300 nm was formed on asilicon substrate having a thickness of 0.725 mm. Samples 1 to 4 of thememory element 3 having the configuration shown in FIG. 3A are formedthereon.

FIG. 4 shows the materials and the film thicknesses of the samples 1 to4. It should be noted that the sample 1 corresponds to a comparativeexample and the samples 2 to 4 correspond to this embodiment.

All the samples 1 to 4 including the comparative example have the sameconfiguration in terms of the following.

Underlying layer 14: Laminated film of a Ta film having a film thicknessof 10 nm and a Ru film having a film thickness of 25 nm

Intermediate layer (tunnel insulating layer) 16: Magnesium oxide filmhaving a film thickness of 0.9 nm

Memory layer 17: CoFeB layer having a film thickness of 1.5 nm

Cap layer 18: Laminated structure of Ta having a film thickness of 3 nm,Ru having a film thickness of 3 nm, and Ta having a film thickness of 3nm

In the samples 1 to 4, the non-magnetic layer 15 is configured asfollows.

The ferromagnetic layer 15 c, the non-magnetic layer 15 b, and theferromagnetic layer 15 a, which form a laminated ferri-pinned structure,have the same configuration in the samples 1 to 4.

Ferromagnetic layer 15 c: CoPt having a film thickness of 2 nm

Non-magnetic layer 15 b: Ru having a film thickness of 0.8 nm

Ferromagnetic layer 15 a: CoFeB having a film thickness of 2 nm

In the sample 1, which is a comparative example, the anti-ferromagneticoxide layer 15 d is not provided.

The sample 2 corresponds to the configuration of FIG. 3C, and Co—Ohaving a film thickness of 0.1 nm is provided on the ferromagnetic layer15 a at the side of the non-magnetic layer 15 b to form theanti-ferromagnetic oxide layer 15 d.

The sample 3 corresponds to the configuration of FIG. 3D, and Co—Ohaving a film thickness of 0.1 nm is provided on the ferromagnetic layer15 c at the side of the non-magnetic layer 15 b to form theanti-ferromagnetic oxide layer 15 d.

The sample 4 corresponds to the configuration of FIG. 3E, and Co—Ohaving a film thickness of 0.1 nm is provided on the ferromagnetic layer15 c at the side of the underlying layer 14 to form theanti-ferromagnetic oxide layer 15 d.

In each sample, the composition of the Co—Fe—B alloy in each of themagnetization-fixed layer 15 (ferromagnetic layer 15 a) and the memorylayer 17 was (Co30%-Fe70%) 80%-B20% (all of which is in atm %).

The magnesium oxide (MgO) film of the intermediate layer 16 and Co—O(anti-ferromagnetic oxide layer 15 d) of the non-magnetic layer 15 wereformed using an RF magnetron sputtering method. Other layers were formedusing a DC magnetron sputtering method.

FIGS. 5A and 5B each show the measurement result of the magnetoopticKerr effect of the sample 1, which is the comparative example, and themeasurement result of the magnetooptic Kerr effect of the sample 2 inthe embodiment, respectively.

The magnetic field of the laminated ferri-coupling H coupling in thecomparative example (sample 1) was 3 kOe. On the other hand, themagnetic field of the laminated ferri-coupling H coupling in theembodiment (sample 2) was 3.8 kOe.

The magnetic field of the laminated ferri-coupling H coupling is definedas a magnetic field in which a laminated ferri-coupling collapses, asshown in the figures.

FIG. 6 shows each of the magnetic field of the laminated ferri-couplingH coupling in the samples 1 to 4.

FIG. 6 reveals that the magnetic field of the laminated ferri-coupling Hcoupling increases by about 1 kOe in the samples 2 to 4 in which Co—O isinserted into the magnetization-fixed layer 15, compared with the sample1 in the comparative example.

It can be confirmed that the magnetic field of the laminatedferri-coupling H coupling is increased according to this embodiment, bycomparing the FIG. 5A and FIG. 5B described above.

In the samples 2 to 4, Co—O as the anti-ferromagnetic oxide layer 15 dis inserted into the top and bottom interfaces of the non-magnetic layer15 b (Ru), or the interface between the ferromagnetic layer 15 c (CoPtlayer) of the magnetization-fixed layer 15 and the underlying layer 14.In any of the cases, the magnetic field of the laminated ferri-couplingH coupling is increased.

Therefore, it is considered that the magnetic field of the laminatedferri-coupling H coupling is increased even if Co—O is inserted into anyof the ferromagnetic layers (CoPt, or CoFeB) of the magnetization-fixedlayer 15.

The mechanism in which the magnetic field of the laminatedferri-coupling H coupling is increased by inserting Co—O is consideredas follows.

In general, Co—O is known as an anti-ferromagnetic material. Forexample, an antiferromagnetic coupling is caused on the interfacebetween Co and Co—O. That is, also in this embodiment, anantiferromagnetic coupling between Co and Co—O is caused near themagnetic layer in which Co—O is inserted. This increases theperpendicular magnetic anisotropy partially.

Therefore, it is considered that the perpendicular magnetic anisotropyof the ferromagnetic layer that forms the magnetization-fixed layer 15is enhanced, which results in an increase in the magnetic field of thelaminated ferri-coupling H coupling through Ru.

If the film thickness of Co—O is too thin, anti-ferromagnetic couplingeffects are reduced, and if the film thickness of Co—O is too thick,resistance of a film increases. Therefore, the film thickness of Co—O isfavorably within a range of 0.05 to 0.3 nm.

In Experiment, although a film that was directly sputtered from a Co—Otarget was used for Co—O, a Co layer may be formed with Ar+oxygen gas,or a thin Co film may be formed to be oxidized.

<5. Alternative>

While the embodiment according to the present disclosure has beendescribed, it should be understood that the present disclosure is notlimited to the layered structure of the memory element 3 shown in theabove-described embodiment, but it is possible to adopt a variety oflayered structures.

For example, although the composition of Co—Fe—B in themagnetization-fixed layer 15 and the memory layer 17 is the same in theembodiment, it should be understood that the present disclosure is notlimited thereto, various structures may be taken without departing fromthe scope and spirit of the present disclosure.

Moreover, although the ferromagnetic layer 15 a (Co—Fe—B layer) in themagnetization-fixed layer 15 is a single-layer in the embodiment, it isalso possible to add an element or an oxide to the ferromagnetic layer15 a unless the coupling magnetic field is significantly decreased.

Examples of elements to be added include Ta, Hf, Nb, Zr, Cr, Ti, V, andW. Examples of oxides to be added include MgO, Al—O, SiO₂.

Moreover, the underlying layer 14 and the cap layer 18 may be formed ofa single material or may have a configuration in which a plurality ofmaterials are laminated.

Moreover, Co—O is described as an anti-ferromagnetic oxide material tobe inserted into the laminated ferri-pinned structure of themagnetization-fixed layer 15, Ni—O, Cr₂O₃, VO₂ may be used for theanti-ferromagnetic oxide layer 15 d.

The memory element 3 according to the embodiment of the presentdisclosure has a configuration of the magnetoresistive effect elementsuch as a Tunneling Magneto Resistance (TMR) element. Themagnetoresistive effect element as the TMR element can be applied to avariety of electronic apparatuses, electric appliances and the likeincluding a magnetic head, a hard disk drive equipped with the magnetichead, an integrated circuit chip, a personal computer, a portableterminal, a mobile phone and a magnetic sensor device as well as theabove-described memory apparatus.

As an example, FIGS. 7A and 7B each show an application of amagnetoresistive effect element 101 having the configuration of thememory element 3 to a composite magnetic head 100. FIG. 7A is aperspective view shown by cutting some parts of the composite magnetichead 100 for discerning the internal configuration. FIG. 7B is across-sectional view of the composite magnetic head 100.

The composite magnetic head 100 is a magnetic head used for a hard diskapparatus or the like. On a substrate 122, the magnetoresistive effectmagnetic head according to the embodiment of the present disclosure isformed. On the magnetoresistive effect magnetic head, an inductivemagnetic head is laminated and thus the composite magnetic head 100 isformed. The magnetoresistive effect magnetic head functions as areproducing head, and the inductive magnetic head functions as arecording head. In other words, the composite magnetic head 100 isconfigured by combining the reproducing head and the recording head.

The magnetoresistive effect magnetic head mounted on the compositemagnetic head 100 is a so-called shielded MR head, and includes a firstmagnetic shield 125 formed on the substrate 122 via an insulating layer123, the magnetoresistive effect element 101 formed on the firstmagnetic shield 125 via the insulating layer 123, and a second magneticshield 127 formed on the magnetoresistive effect element 101 via theinsulating layer 123. The insulating layer 123 includes an insulationmaterial such as Al₂O₃ and SiO₂.

The first magnetic shield 125 is for magnetically shielding a lower sideof the magnetoresistive effect element 101, and includes a soft magneticmaterial such as Ni—Fe. On the first magnetic shield 125, themagnetoresistive effect element 101 is formed via the insulating layer123.

The magnetoresistive effect element 101 functions as a magnetosensitiveelement for detecting a magnetic signal from the magnetic recordingmedium in the magnetoresistive effect magnetic head. Themagnetoresistive effect element 101 may have the similar filmconfiguration to the above-described memory element 3.

The magnetoresistive effect element 101 is formed in an almostrectangular shape, and has one side that is exposed to an oppositesurface of the magnetic recording medium. At both ends of themagnetoresistive effect element 101, bias layers 128 and 129 aredisposed. Also, connection terminals 130 and 131 that are connected tothe bias layers 128 and 129 are formed. A sense current is supplied tothe magnetoresistive effect element 101 through the connection terminals130 and 131.

Above the bias layers 128 and 129, the second magnetic shield 127 isdisposed via the insulating layer 123.

The inductive magnetic head laminated and formed on the above-describedmagnetoresistive effect magnetic head includes a magnetic core includingthe second magnetic shield 127 and an upper core 132, and a thin filmcoil 133 wound around the magnetic core.

The upper core 132 forms a closed magnetic path together with the secondmagnetic shield 127, is to be the magnetic core of the inductivemagnetic head, and includes a soft magnetic material such as Ni—Fe. Thesecond magnetic shield 127 and the upper core 132 are formed such thatfront end portions of the second magnetic shield 127 and the upper core132 are exposed to an opposite surface of the magnetic recording medium,and the second magnetic shield 127 and the upper core 132 come intocontact with each other at back end portions thereof. The front endportions of the second magnetic shield 127 and the upper core 132 areformed at the opposite surface of the magnetic recording medium suchthat the second magnetic shield 127 and the upper core 132 are spacedapart by a predetermined gap g.

In other words, in the composite magnetic head 100, the second magneticshield 127 not only magnetically shields the upper side of themagnetoresistive effect element 101, but functions as the magnetic coreof the inductive magnetic head. The second magnetic shield 127 and theupper core 132 configure the magnetic core of the inductive magnetichead. The gap g is to be a recording magnetic gap of the inductivemagnetic head.

In addition, above the second magnetic shield 127, thin film coils 133buried in the insulation layer 123 are formed. The thin film coils 133are formed to wind around the magnetic core including the secondmagnetic shield 127 and the upper core 132. Both ends (not shown) of thethin film coils 133 are exposed to the outside, and terminals formed onthe both ends of the thin film coil 133 are to be external connectionterminals of the inductive magnetic head. In other words, when amagnetic signal is recorded on the magnetic recording medium, arecording current will be supplied from the external connectionterminals to the thin film coil 133.

The composite magnetic head 121 as described above is equipped with themagnetoresistive effect magnetic head as the reproducing head. Themagnetoresistive effect magnetic head is equipped, as themagnetosensitive element that detects a magnetic signal from themagnetic recording medium, with the magnetoresistive effect element 101to which the technology according to the present disclosure is applied.As the magnetoresistive effect element 101 to which the technologyaccording to the present disclosure is applied shows the excellentproperties as described above, the magnetoresistive effect magnetic headcan achieve further high recording density of magnetic recording.

The present disclosure may also have the following configurations.

(1) A memory element, including

a layered structure including

-   -   a memory layer that has magnetization perpendicular to a film        face in which a direction of the magnetization is changed        depending on information, the direction of the magnetization        being changed by applying a current in a lamination direction of        the layered structure to record the information in the memory        layer,    -   a magnetization-fixed layer that has magnetization perpendicular        to a film face that becomes a base of the information stored in        the memory layer, has a laminated ferri-pinned structure        including at least two ferromagnetic layers and a non-magnetic        layer, and includes an anti-ferromagnetic oxide layer formed on        any of the at least two ferromagnetic layers, and    -   an intermediate layer that is formed of a non-magnetic material        and is provided between the memory layer and the        magnetization-fixed layer.

(2) The memory element according to (1) above, in which

one of the ferromagnetic layers in the magnetization-fixed layer, whichcomes into contact with the intermediate layer, includes Co—Fe—B as amagnetic material.

(3) The memory element according to (1) or (2) above, in which

the anti-ferromagnetic oxide layer is a Co—O layer.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A layered structure, comprising: a memory layerhaving magnetization perpendicular to a film face in which a directionof the magnetization is configured to be changed according toinformation by applying a current in a lamination direction of thelayered structure; a magnetization-fixed layer having magnetizationparallel or antiparallel to the magnetization direction of the memorylayer and comprising a laminated ferripinned structure including aplurality of ferromagnetic layers and one or more non-magnetic layers,and including a layer comprising an antiferromagnetic material formed ona first ferromagnetic layer of the plurality of ferromagnetic layers andsituated between the first ferromagnetic layer and the non-magneticlayer; and a tunnel insulating layer located between the memory layerand the magnetization-fixed layer.
 2. The layered structure of claim 1,wherein the tunnel insulating layer comprises MgO.
 3. The layeredstructure of claim 1, wherein at least one of the one or morenon-magnetic layers is formed from Ru.
 4. The layered structure of claim1, wherein the at least one layer is formed from Co—O.
 5. The layeredstructure of claim 1, wherein the layer comprising an antiferromagneticmaterial comprises an antiferromagnetic oxide.
 6. The layered structureof claim 1, wherein at least one of the plurality of ferromagneticlayers includes Co—Fe—B.
 7. A memory apparatus, comprising: a memoryelement configured to store information based at least in part on amagnetization state of a magnetic material, the magnetic materialcomprising: a memory layer having magnetization perpendicular to a filmface in which a direction of the magnetization is configured to bechanged according to information by applying a current in a laminationdirection of the layered structure, the memory layer comprising Co, Feand B; a magnetization-fixed layer having magnetization parallel orantiparallel to the magnetization direction of the memory layer andcomprising a plurality of ferromagnetic layers and one or morenon-magnetic layers, and including a layer comprising anantiferromagnetic material formed on a first ferromagnetic layer of theplurality of ferromagnetic layers and situated between the firstferromagnetic layer and the non-magnetic layer; and a tunnel insulatinglayer comprising MgO, located between the memory layer and themagnetization-fixed layer.
 8. The layered structure of claim 7, whereinthe layer comprising an antiferromagnetic material comprises Ru.
 9. Thelayered structure of claim 8, wherein the layer comprising the firstferromagnetic layer comprises Co, Fe, and B.
 10. The layered structureof claim 8, wherein the layer comprising the first ferromagnetic layercomprises Co and Pt.
 11. A memory apparatus, comprising: a memoryelement configured to store information based at least in part on amagnetization state of a magnetic material, the magnetic materialcomprising: a memory layer having magnetization perpendicular to a filmface in which a direction of the magnetization may be changed accordingto information by applying a current in a lamination direction of thelayered structure to record the information in the memory layer; amagnetization-fixed layer having magnetization parallel or antiparallelto the magnetization direction of the memory layer and comprising alaminated ferripinned structure that includes a plurality offerromagnetic layers and one or more non-magnetic layers, at least onelayer of the ferripinned structure being formed from anantiferromagnetic material that provides an increased laminatedferri-coupling of the ferripinned structure than would be provided inthe absence of the at least one layer; and a tunnel insulating layerlocated between the memory layer and the magnetization-fixed layer.